A conventional optical moving or motion picture projector may include a light source, an input image device holder, such as a film guide, sprockets, shutter, etc., or by which a film, and particularly the frames thereof, may be placed for illumination by light from the light source, and a lens system for projecting an image of the illuminated frame. Typically the film would have optically transparent portions and optically absorbent portions, e.g., black and/or colored portions. When projected onto a screen, such black portions appear black due to absorption of light by the light absorbing, e.g., black emulsion, material, and the optically transmissive portions would appear relatively bright on the screen. Common exemplary projectors are of 8, 16, and 32 millimeter sizes, depending on the size of the film used.
One problem with conventional projectors is the large amount of heat that is absorbed by the light absorbing portions of the film, which could cause destruction or damage to the film; to minimize such heat build-up it often is necessary to use one or more infrared or heat absorbing filters optically upstream of the film. The heat dissipated in the heat filters and at the optical source or cabinet containing the same requires elimination, for example by a blower or other means. The blower may produce undesirable noise and/or vibration and uses energy that would not have to be consumed if the heat did not require such elimination. A further disadvantage of conventional projectors is the diffraction of light at the interface between light absorbing material, such as a black emulsion, and transparent material of the film; such diffraction can reduce the contrast and quality of the projected image seen on a screen. Furthermore, in conventional film projectors, contrast would be reduced since images are formed in part, at least, by the blockage of light, and such blockage is a function of absorption, which can vary, depending on the quality of opaqueness of the blocking material. Other disadvantages of conventional motion picture projectors is the size and number of reels of film needed to project an entire motion picture, story, etc., due to the relatively fixed nature of the respective images and scenes in the film.
Liquid crystal material currently is used in a wide variety of devices, including, for example, optical devices such as visual displays. A property of liquid crystal material enabling use in visual displays is the ability to scatter and/or to absorb light when the liquid crystal structure is in a random alignment and the ability to transmit light when the liquid crystal structure is in an ordered alignment.
Frequently a visual display using liquid crystal material displays dark characters on a gray or relatively light background. In various circumstances it would be desirable, though, using liquid crystal material to be able to display with facility relatively bright characters or other information, etc. on a relatively dark background. It would be desirable as well to improve the effective contrast between the character displayed and the background of the display itself.
Examples of electrically responsive liquid crystal material and use thereof are found in the above patents and applications.
Currently there are three categories of liquid crystal materials, namely cholesteric, nematic and smectic. In one embodiment of the present invention nematic liquid crystal material, a combination of nematic and some cholesteric type or smectic type is used. More specifically, the liquid crystal material preferably is operationally nematic or operationally smectic, i.e. it acts generally as nematic or smectic material and not as the other types. Operationally nematic means that in the absence of external fields structural distortion of the liquid crystal is dominated by the orientation of the liquid crystal at its boundaries, e.g. with a surface, such as the surface of a capsule-like volume, rather than bulk effects, such as very strong twists as in cholesteric material, or layering as in smectic material. Thus, for example, chiral ingredients which induce a tendency to twist but cannot overcome the effects of boundary alignment still would be operationally nematic. Such material should have a positive dielectric anistropy. Although various characteristics of the various liquid crystal materials are described in the prior art, one known characteristic is that of reversibility. Particularly, nematic liquid crystal material is known to be reversible (and that characteristic is desirable in the present invention), but cholesteric material ordinarily is not reversible.
In another embodiment of the invention smectic or operationally smectic liquid crystal material or a combination of liquid crystal materials that operate as smectic liquid crystal material may be used. A characteristic of smectic liquid crystal material making it useful in the present invention is structural storage or memory capability of such material, i.e., the ability to retain a particular alignment configuration until specifically reset to another alignment configuration. Another characteristic is the responsiveness to electric field to align with respect thereto.
It is also known to add pleochroic dyes to the liquid crystal material. One advantage to using pleochroic dye with the liquid crystal material is the eliminating of a need for a polarizer. However, in the nematic form a pleochroic device has relatively low contrast. In the past cholesteric material could be added to the nematic material together with the dye to improve contrast ratio. See for example the White et al article in Journal of Applied Physics, Vol. 45, No. 11, Nov. 1974, at pages 4718-4723. However, although nematic material is reversible, depending on whether or not an electric field is applied across the same, cholesteric material ordinarily would not tend to its original zero field form when the electric field would be removed and this characteristic may detrimentally affect the quality of a display that uses nematic and cholesteric liquid crystal and pleochroic dye. For example, a disadvantage to use of pleochroic dye in solution with liquid crystal material is that the absorption of the dye is not zero in the field-on condition; rather, absorption in the field-on condition follows an ordering parameter, which relates to or is a function of the relative alignment of the dyes.
Usually liquid crystal material is anisotropic both optically (birefringence) and, for example in the case of nematic material, electrically. In optically anisotropic liquid crystal material there is a difference between the ordinary index of refraction and the extraordinary index of refraction the liquid crystal material. The optical anisotropy is manifest by the scattering of light when the liquid crystal material is in random alignment, and the transmission of light through the liquid crystal material when it is in ordered alignment. The electrical anisotropy may be a relationship between the dielectric constant or dielectric coefficient with respect to the alignment of the liquid crystal material.
In the past, devices using liquid crystals, such as visual display devices, have been relatively small. Use of encapsulated liquid crystals disclosed in applicant's above mentioned patents and co-pending applications has enabled the satisfactory use of liquid crystals in relatively large size displays, such as billboards, etc., and another large (or small) scale use may be as an optical shutter to control passage of light from one area into another, say at a window or window-like area of a building. The present invention relates to improvements in such encapsulated liquid crystals using the same as a device on which plural frames can be created to represent an image or characteristics of an image and to the utilization of the light scattering and transmitting characteristic of the liquid crystal material for projection purposes.
As used herein with respect to the present invention, encapsulated liquid crystal material means liquid crystal material in a containment medium with a surface for distorting the natural structure of the liquid crystal in the absence of a prescribed input to cause scattering of incident light. Thus, a quantity of liquid crystal material is contained in a volume or volumetric space in the containment medium. The respective volumetric spaces may be substantially closed, may be capsule-like, may be like cells in stable emulsion or matrix, and/or may be interconnected with other volumetric spaces, and so on. According to a preferred embodiment, the encapsulated liquid crystal material is represented by a plurality of volumes of liquid crystal in a containment medium formed as an emulsion of the liquid crystal material and the containment medium. Such emulsion should be a stable one. Various methods for making and using encapsulated liquid crystal material and apparatus associated therewith are disclosed below and in applicant's patents and co-pending patent applications, which are incorporated by reference.
Liquid crystal projectors and projection optics are disclosed in applicant's above-mentioned U.S. Pat. No. 4,613,207. Liquid crystal imagers which create an image or characteristics of an image using charge storage techniques are disclosed in applicant's above-mentioned U.S. Pat. No. 4,603,945. The present invention relates to a liquid crystal motion or moving picture projector utilizing such projectors and projection optics and charge storage and other imager techniques, and/or structural storage imager techniques to create a plurality of images or characteristics of images capable of sequential projection by the projector. Structural storage imager technique relies on the ability of the liquid crystal to maintain or to store a particular alignment of liquid crystal structure until a further input, such as heat (or thermal, the two terms being used equivalently herein) or electrical input, is applied thereto.
As used herein, the terms liquid crystal display and liquid crystal imager are intended to be equivalent and interchangeable. The liquid crystal display or imager creates the image or the characteristics of the image intended to be projected by the projector or projection optics.